Method for inducing ventricular arrhythmias in an animal model system

ABSTRACT

A method is described for increasing the likelihood of the occurrence of an arrhythmia in a heart, particularly a ventricular arrhythmia of the type leading to Sudden Cardiac Death. The method includes the steps of creating an atrioventricular block in the heart of an animal test subject, inducing a myocardial infarction in the heart of the test subject, and then stimulating myocardial hyperinnervation the test subject. In a specific example described herein, the atrioventricular block is created by ablating the atrioventricular node of the heart using an ablation catheter. The myocardial infarction is induced by ligating the left anterior descending portion of the coronary artery. Myocardial hyperinnervation is stimulated by application of Nerve Growth Factor or other neurotrophic vectors to the left stellate ganglion. The test subject is an adult canine. By creating an atrioventricular block and a myocardial infarction within the heart of an adult canine test subject, then stimulating nerve growth within the left stellate ganglion of the subject using Nerve Growth Factor, it has been found that there is a significant increase in the likelihood of Sudden Cardiac Death arising from ventricular arrythmias. It is believed that the Sudden Cardiac Death of the test subject arises in a manner very similar to circumstances wherein Sudden Cardiac Death occurs in human patients subject to a previous myocardial infarction, thus, an animal model system for artificially inducing a heart arrhythmia is disclosed. Thus, the method and animal model system facilitate the collection of data pertinent to conditions within the heart arising prior to Sudden Cardiac Death and for developing and testing therapies intended to prevent Sudden Cardiac Death.

FIELD OF THE INVENTION

The invention generally relates to techniques for inducing heartarrhythmias in animal test subjects and in particular to techniques forinducing ventricular arrhythmias of the type that can result in SuddenCardiac Death.

BACKGROUND OF THE INVENTION

Sudden Cardiac Death (“SCD”) claims about 300,000 lives a year in theUnited States alone. In most cases, the direct cause of SCD is aventricular tachycardia (“VT”) which triggers a ventricular fibrillation(“VF”). VT and VF are different types of ventricular arrhythmias. VT isan abnormally fast ventricular heart rhythm which is, by itself,typically not fatal. VF is a chaotic ventricular heart rhythm whichproduces little or no net blood flow from the heart, such that there islittle or no net blood flow to the brain and other organs. VF, if notterminated, results in death. In most cases of SCD, the victim has aprevious myocardial infarction (“MI”), i.e. the patient had a previousheart attack caused by blockage of a portion of the coronary arterywhich supplies blood to the heart muscle. As a result of the blockage, aportion of the heart muscle does not receive blood and therefore becomesscarred and diseased. The scarred and diseased portion of the heart isreferred to as the MI. For several days immediately subsequent to theoccurrence of an MI, numerous episodes of VT—referred to as phase oneepisodes-typically occur. Eventually, the phase one VT episodes largelydisappear. Several days or weeks later, though, additional episodes ofVT—referred to as phase two episodes-typically begin to occur. It is thephase two episodes of VT that often transition to VF resulting in SCD ofthe patient

Accordingly, it would be highly desirable to develop techniques forpreventing VT from occurring, particularly phase two VT in a patientshaving an MI and, if VT does occur, for preventing the VT fromtransitioning to a VF. One technique employed in an attempt to preventVT from occurring is overdrive pacing of the heart. With overdrivepacing, the heart is paced at a rate higher than its intrinsic pacingrate. If VT nevertheless occurs, one or more electrical cardioversionpulses are typically applied to the heart in an attempt to terminate theVT so that the VT does not transition to VF. If VF nevertheless occurs,one or more stronger electrical defibrillation pulses are typicallyapplied to the heart in an attempt to terminate the VF therebypreventing SCD. Hence, for patients that have an MI, particularly asignificant one, an implantable cardioverter-defibrillator (ICD) isoften implanted into the patient. The ICD includes components foroverdrive pacing the heart and for detecting VT or VF and foradministering the appropriate therapy. However, the need to frequentlyoverdrive pace the heart and to deliver cardioversion or defibrillationpulses can quickly deplete the battery power of the ICD requiringfrequent replacement. Also, the therapies administered by the ICD,particularly the application of cardioversion pulses, may be extremelypainful to the patient. Moreover, in some cases, the conventionaltherapy provided by the ICD is not sufficient to prevent or terminate VFand, accordingly, the patient succumbs to SCD.

Hence, it would also be highly desirable to develop new and moreeffective techniques for predicting and preventing VT from occurring,particularly prevention techniques that do not require frequentoverdrive pacing. For example, it would be desirable to provide atechnique for predicting when an episode of VT is imminent such thatoverdrive pacing, or other therapies, need only be applied incircumstances when VT is likely to occur. A reliable predictiontechnique could greatly reduce need for overdrive pacing, therebysubstantially extending the lifetime of the power supply of the ICD andeliminating the need for frequent surgical replacement of the batterysupply. Most importantly, with reliable VT prediction, techniques forpreventing the occurrence of VT may prove to be more reliable, thusreducing the number of episodes of VT and consequently reducing the needfor cardioversion therapy and reducing the risk that the VT maytransition to VF if cardioversion fails.

It would also be highly desirable to develop new and more effectivetechniques for predicting and preventing VT from transitioning to VF,preferably without the need for cardioversion pulses. For example, itwould be desirable to provide a technique for predicting when an episodeof VT is likely to transition to VF such that cardioversion therapy needonly be applied when there is a significant risk that the transitionwill occur. A reliable prediction technique could greatly reduce theneed for cardioversion therapy which, as noted, can be extremely painfulto the patient. Also the lifetime of the power supply of the ICD isfurther extended thus reducing the need for surgical replacementprocedures. Most importantly, with reliable VF prediction, techniquesfor preventing the occurrence of VF may prove to be more reliable, thusreducing the number of episodes of VF and consequently reducing the needfor defibrillation therapy and reducing the risk of SCD ifdefibrillation fails.

The new and more effective prediction or prevention techniques couldtake the form of new detection or analysis techniques performed by theICD, or new therapies administered by the ICD. Alternatively, thetechniques could take the form of therapies not requiring implantationof an ICD, such as application of new drug therapies and the like.Considerable research is ongoing in these areas.

A significant problem, however, is that there is currently no effectivetechnique for inducing ventricular arrhythmias in test animals,particularly ventricular arrhythmias of the type resulting in SCD, insuch a manner that permits effective testing of techniques intended topredict and prevent the arrhythmias to thereby prevent SCD. Morespecifically, it would be highly desirable to provide a technique forinducing VT or VF within test animals which would permit researchers toanalyze conditions within the heart leading up to VT or VF for thepurposes of identifying conditions which might serve to predict VT orVF. A technique for reliably inducing VT or VF within test animals,would also assist researchers in developing and testing new techniquesfor preventing VT or VF from occurring and for evaluating the efficacyof such techniques. As one example, therapies for the purposes ofpreventing VT from transitioning to VF without requiring a cardioversionpulse could be tested by implanting an ICD within an animal testsubject, then inducing VT to thereby verify that the ICD reliablyprevents the VT from transitioning to VF and thereby prevents or atleast reduces the risk of SCD. Such tests would also prove helpful ingaining government approval for marketing ICD's or other implantablemedical devices intended to prevent SCD.

More specifically, there appear to be no effective techniques forinducing VT or VF within test animals which effectively reproduce theconditions with which SCD typically occurs in human patients, i.e.,phase two VT to VF transitions within patients subject to a previous MI.One conventional technique, for example, requires applying electricalstimulation pulses to the heart to artificially induce VT. However, ifVT is artificially induced by application of electrical pulses, anycharacteristics of naturally occurring VT which could act as a reliablepredictor of a subsequent transition to VF are difficult, and perhapsimpossible, to detect. Likewise, techniques intended to prevent the VTto VF transition are difficult to test in circumstances where artificialelectrical pulses are simultaneously being applied to the heart. Rather,reliable testing of techniques for predicting and preventing a VT to VFtransition are best performed if the VT to VF transition arises insubstantially the same manner in which it would naturally arise withinpatients, particularly those patients already subject to an MI.

Another conventional technique for artificially inducing SCD within testanimals, is to create an acute ischemia sufficient to induce VT. Anacute ischemia is a complete or nearly complete loss of blood supply tothe heart typically resulting in a massive MI and death of the testsubject. Techniques intended to predict or prevent a VT or a VF withinpatients having a mild MI may not be effectively tested in circumstanceswhere a much more severe ischemia is imposed upon the heart of the testanimal. Furthermore, many SCD episodes are not associated with anyevidence of ischemia. Therefore, induction of SCD by ischemia does notnecessarily simulate what actually happens in patients.

Thus, it would be highly desirable to provide a technique for inducingarrhythmias in animal test subjects, which induces the arrhythmias in amanner similar to which arrhythmias normally occur within humanpatients. In particular, it would be highly desirable to provide atechnique for inducing ventricular arrhythmias of the type leading toSCD in patients having a previous MI. It is to these ends that theinvention is primarily directed.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method is provided forincreasing the likelihood of the occurrence of an arrhythmia in a heart,particularly a ventricular arrhythmia of the type leading to SCD. Themethod includes the steps of creating an atrioventricular (AV) block inthe heart of an animal test subject, inducing an MI in the heart of thetest subject, and then stimulating myocardial hyperinnervation in thetest subject.

In an exemplary embodiment of the method, the AV block is created byablating the AV node of the heart using an ablation catheter. The MI isinduced by ligating the left anterior descending portion of the coronaryartery. Myocardial hyperinnervation is stimulated by application ofnerve growth factor (“NGF”) or other neurotrophic vectors to the leftstellate ganglion. Alternatively, electrical stimulation signals areapplied to the left stellate ganglion. The test subject may be, forexample, an adult canine.

By creating an AV block and an MI within the heart of an adult caninetest subject, then stimulating nerve growth within the left stellateganglion of the subject using NGF, it has been found that there is asignificant increase in the likelihood of SCD arising from phase twoventricular arrhythmias. It is believed that the SCD of the test subjectarises in a manner very similar to circumstances wherein SCD occurs inhuman patients subject to a previous MI. Thus, the method permits SCD tobe induced within test animals in a manner facilitating the collectionof data pertinent to conditions within the heart arising prior to SCDand for testing techniques intended to prevent SCD, particularlytechniques intended to prevent phase two VT and VF within patientssubject to a previous MI. Hence, other aspects of the invention aredirected to methods for collecting data pertinent to predictors ofarrhythmias, particularly phase two VT and VF in patients subject to aprevious MI, to facilitate development of techniques for predicting andpreventing the arrhythmias. Still other aspects of the invention aredirected to methods for testing techniques intended to predict orprevent the onset of arrhythmias, again particularly phase two VT and VFin patients subject to a previous MI. An animal model system forartifically inducing a heart arrhythmia is also provided. Still otherobjects, advantages and features of the invention will be apparent fromthe detailed descriptions which follow in combination with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a stylized representation of an animal test subject having anosmotic pump and ICD implanted therein and particularly illustrating theheart and left stellate ganglion of the test subject.

FIG. 2 illustrates a method for inducing ventricular arrhythmias in theanimal test subject of FIG. 1 and for testing the ICD to verify that theICD properly predicts or prevents the arrhythmias.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring to the figures, various techniques for inducing ventriculararrhythmias of the type leading to SCD within animal test subjects willnow be described. The techniques for inducing ventricular arrhythmiasare described primarily with reference to the testing of therapiesintended to prevent SCD, wherein the therapies are administered by anICD. However, the techniques for inducing ventricular arrhythmias arealso applicable to a wide range of other practical applications such asthe testing of therapies that do not involve ICD's.

Briefly, in one example, the technique for inducing ventriculararrhythmias involves creating an AV block in the heart of an animal testsubject, inducing an MI in the test subject and stimulatinghyperinnervation in the left stellate ganglion of the test subject bypumping NGF or other neurotrophic vector into the ganglion using anosmotic pump. FIG. 1 is a stylized illustration of an animal testsubject, particularly illustrating the heart and left stellate ganglionof the subject. FIG. 1 also illustrates an ICD 10 having a lead 12coupled to the heart and an osmotic pump 14 positioned near the leftstellate ganglion. Osmotic pump 14 continuously infuses the leftstellate ganglion with NGF to stimulate nerve sprouting therein which,as will be described below, increases the likelihood of ventriculararrhythmias, particularly arrhythmias of the type possibly leading toSCD. ICD 10 is programmed to predict and prevent the ventriculararrhythmias in the heart of the test subject. To this end, the ICDdetects and records electrical signals from the heart using lead 12 and,if necessary, applies therapy to the heart using the lead. The programsof the ICD are preferably newly developed prediction or preventiontechniques in need to test verification. A test analysis system 16,which may include a conventional ICD programmer device or othercomputing device, interrogates the ICD using a telemetry system 18 todownload the recorded heart signals for analysis for determining whetherthe ICD properly predicts and prevents ventricular arrhythmias.

The techniques for inducing ventricular arrhythmias in animal testsubjects and for testing techniques intended to predict or prevent thearrhythmias will now be described in detail with reference to FIG. 2.Initially, at step 100; an ICD is programmed to detect and analyzeelectrical heart signals and to attempt to predict therefrom theoccurrence of arrhythmias, particularly ventricular arrhythmias that maylead to SCD. The ICD is also programmed to apply therapy in an attemptto prevent the ventricular arrhythmias from occurring and therebyprevent SCD. The specific ICD programming for predicting or preventingventricular arrhythmias may be consistent with conventional techniques.Preferably, though, the ICD is programmed to implement newly developedtechniques for prediction or prevention of arrhythmias.

As far as conventional prediction techniques are concerned, the ICD maybe programmed to predict whether VF is imminent by detecting theoccurrence of VT and then determining the rate of the VT. If the rate isabove a certain threshold, the ICD concludes that a transition to VF islikely. Prevention of VF may then be attempted using conventionalcardioversion therapy. As far as conventional prevention techniques areconcerned, the ICD may be programmed to overdrive pace the heart in anattempt to prevent the occurrence of phase two VT. A wide range of otherconventional prediction or prevention techniques may be employed.

Newly developed techniques for prediction or prevention of ventriculararrhythmias may exploit unique characteristics of heart signalsoccurring prior to the onset of VT or perhaps occurring during VT butprior to a transition to VF. As can be appreciated, a wide variety oftechniques for predicting or preventing ventricular arrhythmias may beprogrammed for use with the ICD. The ICD may be programmed to performmultiple concurrent techniques. The ICD may additionally perform otherfunctions, such as anti-bradycardia pacing, not specifically targetedfor the prediction or prevention of ventricular arrhythmias leading toSCD.

At step 102, an animal test subject such as an adult mongrel canine isselected and, at step 104, the ICD is implanted within the test subjectand appropriate leads are connected to the heart of the subject. At step106, a complete AV block is created within the heart of the animal testsubject by ablation of the AV node using a radio frequency catheter, orother appropriate device or technique. If the animal test subject is anadult canine, the heart typically continues to beat without the need forany pacing. For other animal test subjects, pacing may be required.Accordingly, in such subjects, the ICD should be programmed to providethe appropriate pacing. For adult canines, the AV node is preferablycompletely ablated to provide a total AV block. For other animal testsubjects, a partial AV block may suffice and, indeed, for some animaltest subjects it is possible that other aspects of the inventiondescribed herein are sufficient to reliably induce ventriculararrhythmias without any AV blockage. The identification of such testsubjects, if any, is achieved using routine techniques such as byexperimenting with different test subjects, some having a complete AVblock and others having only partial or non-existent AV blocks.

At step 108, the left anterior descending coronary artery of the animaltest subject is completely ligated below the first diagonal branch tocreate an MI. Alternative techniques for blocking the coronary artery tocreate an MI include injecting certain block-inducing chemicals into theartery or positioning wires or other blocking devices into the arteryusing a catheter. For adult canines, it has been found that theaforementioned ligation typically results in an MI involving about 14%of the heart of the animal test subject and that a 14% MI is effectivefor the purposes of the invention. Other degrees of MI may be found tobe effective in adult canines as well including, for example, MI'sinvolving between 10 to 30 percent of the heart. For some animal testsubjects, a larger or smaller MI may be desirable. Depending upon theparticular animal test subject, it may be desirable to provideadditional or alternative ligation points within the coronary artery. Ascan be appreciated though, an MI affecting too great a portion of theheart of the animal test subject may result in immediate termination ofthe test subject, thereby preventing testing of the programs implementedby the ICD. Routine testing of various animal test subjects and ofvarious locations for coronary artery ligation may be employed todetermine an optimal amount of MI within selected animal test subjectsso as to provide the highest likelihood of inducing ventriculararrhythmias of the type leading to SCD within the test subject.

At step 110, an osmotic pump is implanted within the animal test subjectin the vicinity of the left stellate ganglion. Alternatively, electrodesare positioned in the vicinity of the left stellate ganglion. At step112, the left stellate ganglion is continuously infused with NGF, orother neurotrophic vector, using the osmotic pump for the purposes ofstimulating nerve sprouting or other forms of hyperinnervation withinthe left stellate ganglion or within the vicinity thereof. Othersuitable neurotrophic vectors include neurotrophic chemicals,substances, hormones, etc. If electrodes are used, a low levelelectrical current is continuously conducted between the electrodes forthe purposes of inducing nerve sprouting. Although continuousstimulation is preferred, intermittent or periodic stimulation maysuffice for some test subjects. Also, although the stimulation of nervesprouting in the left stellate nerve ganglion of adult canines has beenfound to be effective for the purposes of the invention, othermyocardial nerve conduction areas may be effective as well in adultcanines or in other animal test subjects. Routine experimentation may beperformed to identify optimal locations for nerve hyperinnervationwithin the myocardial nerve pathways for different selected testanimals. Also, depending upon the test subject, it may be desirable toprovide both neurotrophic vector infusion and electrical stimulationeither simultaneously or alternatingly. Other techniques or compoundsfor stimulating hyperinnervation may be found to be effective as well,in addition to neurotrophic vectors and electrical currents. Also, itmay suffice for some test subjects to inject neurotrophic vectors intothe left stellate ganglion rather than using an osmotic pump. Forelectrical stimulation, optimal current levels are determined by routineexperimentation.

Thus, steps 106 and 112 serve to create a complete AV block and a mildMI in the animal test subject and to further induce myocardialhyperinnervation in the left stellate ganglion. It has been found thatthese steps result in a significant increase in the occurrence ofventricular arrhythmias of the type leading to SCD, specifically phasetwo VT and VF, within adult canine test subjects. It is believed thatthe ventricular arrhythmias induced as a result of steps 106-112 in amanner similar to those occurring within human patients subject to aprior MI and subject to complete or partial AV block. As such, theprograms of the ICD can be tested in conditions closely resembling theconditions in which the ICD may need to operate if implanted in a humanpatient. Accordingly, simultaneous with step 112, step 114 is performedwherein the ICD monitors, analyzes and records conditions within theheart of the animal test subject and attempts to predict and preventventricular arrhythmias. Ultimately, at step 116, a determination ismade as to whether the techniques performed by the ICD are effective,particularly techniques for preventing phase two VT and, if phase two VTnevertheless occurs, for preventing a transition to VF. If thetechniques performed are not effective, such as if the ICD fails toprevent SCD within the animal test subject, the techniques aresubsequently analyzed to determine the reasons for failure, perhapsresulting in adjustment of parameters used in connection with theprogramming of the ICD. If, on the other hand, SCD does not occur, thisprovides evidence as to the efficacy of the programs of the ICD. Ofcourse, testing of the ICD is preferably performed against a suitablylarge population of animal test subjects to achieve statisticallysignificant test results.

Whether or not SCD ultimately occurs, signals recorded during step 114may be analyzed for the purpose of identifying any unique patternswithin the heart signals which may serve as predictors for subsequentepisodes of ventricular arrhythmia. For example, analysis of heartsignals of a large number of animal test subjects wherein phase two VToccurs may reveal a correlation between certain features of the pre-VTheart signals and the subsequent occurrence of VT. If so, an ICD can beprogrammed to predict imminent VT in human patients based upon adetection of similar features of the heart signal and to applypreventative therapy, such as overdrive pacing, only if VT is predicted.Hence, unnecessary overdrive pacing is avoided. As another example,analysis of heart signals of a large number of animal test subjectswherein a VT to VF transition occurs may reveal a correlation betweencertain features of the pre-transition heart signals and the subsequenttransition from VT to VF. If so, an ICD can be programmed to predict theimminent transition to VF in human patients based upon a detection ofsimilar features of the pre-transition heart signal and to applypreventative therapy, such as aggressive cardioversion therapy, only ifthe transition to VF is expected. Hence, unnecessary cardioversiontherapy is avoided. By using these and other predictive techniques, thelifetime of the power supply of the ICD can be extended and pain ordiscomfort associated with unnecessary therapy can be avoided.

Thus, the ventricular arrhythmias induced using steps 106-112 arehelpful both for the purposes of testing techniques for predicting orpreventing the arrhythmias and also for developing a database of heartsignals prior to the occurrence of the arrhythmias for the purposes ofdeveloping new predictive and preventative techniques. Steps 106-112need not be implemented only in connection with testing ICD therapies.Rather the techniques maybe implemented for use in testing a wide rangeof other predictive and preventative techniques, such as new drugtherapies and the like.

As noted, for adult canine animal test subjects, hyperinnervation withinthe left stellate ganglion induced by NGF in combination with a completeAV block and a relatively mild MI has been found to significantlyincrease the likelihood of SCD within the animal test subjects. Theincrease in the likelihood of ventricular arrhythmias is believed tooccur for the following reasons. It appears that an increase insympathetic nerve activity may result in an increase in the likelihoodof the ventricular arrhythmias. By inducing myocardial nerve sprouting,an increased myocardial sensitivity to sympathetic stimulation may occurthus increasing the likelihood of ventricular arrhythmias. Accordingly,to reduce the risk of SCD in human patients, it may be desirable toprevent nerve sprouting, particularly in the left stellate ganglion, forpatients who have had an MI, and in particular for patients also havingan AV block.

However, regardless of the particular mechanism from which the increasedrisk of SCD arises, the technique of the invention has been foundeffective in experiments conducted in connection with adult canines forstatistically increasing the likelihood of SCD. The increase inlikelihood of SCD was detected as compared to control subjects havingonly the MI and AV block, but not the myocardial hyperinnervation. Anincrease in the likelihood of phase two VT and VF episodes was alsoobserved. In all subjects, a comparatively large number of phase one VTepisodes was found to occur within five to ten days following creationof the MI within the test subjects. The occurrence of a large number ofphase one VT episodes immediately following an MI is well known.

What has been described are various techniques for increasing thelikelihood of ventricular arrhythmias in animal test subjects,particularly phase two VT arrhythmias of the type that often trigger VFand consequently SCD. Aspects of the techniques have been describedprimarily with reference to the flowchart of FIG. 2. Each block withinthe flowchart illustrates both a method step and an apparatus elementfor performing the method step. Specific method steps may be performed,as described above, using an ICD, osmotic pump, ablation catheter,coronary artery ligature or other suitable devices. Many of the methodsteps need not necessarily be performed in the order illustrated. Forexample, the order in which the AV block and MI are created can bereversed. As another example, the order in which the osmotic pump andICD are implanted can also be reversed.

In general, the method and apparatus embodiments illustrated withreference to the drawings and described herein are merely illustrativeof principles of the invention which may be implemented in alternativeembodiments to achieve other ends than those specifically describedherein.

I claim:
 1. A method for increasing a likelihood of an occurrence of anarrhythmia in the heart of an animal test subject, said methodcomprising the steps of: creating an AV block in the heart of the testsubject; inducing a myocardial infarction in the heart of the testsubject; selecting a portion of the myocardium of the test subjectwherein hyperinnervation is effective for increasing the likelihood ofthe arrhythmia; and stimulating myocardial hyperinnervation in theselected portion of the myocardium of the test subject.
 2. The method ofclaim 1 wherein the selected portion of the myocardium includes the leftventricle and wherein the step of stimulating myocardialhyperinnervation in the selected portion is performed by stimulatingnerve growth in the left stellate ganglion of the test subject.
 3. Themethod of claim 1 wherein the selected portion of the myocardiumincludes the left ventricle and wherein the step of stimulatinghyperinnervation in the selected portion is performed by applying aneurotrophic vector to a myocardial nerve pathway leading to the leftventricle of the test subject.
 4. The method of claim 3 wherein theneurotrophic vector is selected from the group consisting of NerveGrowth Factor, neurotrophic chemicals, neurotrophic substances andneurotrophic hormones.
 5. The method of claim 1 wherein the selectedportion of the myocardium includes the left ventricle and wherein thestep of stimulating hyperinnervation in the selected portion isperformed by applying electrical stimulation signals to the leftstellate ganglion of the test subject.
 6. The method of claim 1 whereinthe selected portion of the myocardium includes the left ventricle andwherein the step of stimulating hyperinnervation in the selected portionis performed by applying electrical stimulation signals to a myocardialnerve pathway leading to the left ventricle of the test subject.
 7. Themethod of claim 1 wherein the step of creating AV block is performed byrendering the AV node of the heart non-functional.
 8. The method ofclaim 1 wherein the step of creating AV block is performed by ablatingthe AV node of the heart.
 9. The method of claim 1 wherein the step ofinducing a myocardial infarction is performed by blocking a portion ofthe coronary artery of the heart.
 10. The method of claim 9 wherein thecoronary artery is blocked along the left anterior descending portion ofthe coronary artery.
 11. The method of claim 9, wherein the portion ofthe coronary artery is permanently blocked by a technique selected fromthe group consisting of ligating the artery, injecting chemicals intothe artery, and positioning wires in the artery using a catheter. 12.The method of claim 1 wherein the step of inducing a myocardialinfarction is performed to induce a myocardial infarction within 10 to30 percent of the heart tissue mass.
 13. The method of claim 1 whereinthe arrhythmia includes ventricular tachycardia.
 14. The method of claim1 wherein the arrhythmia includes ventricular fibrillation.
 15. A methodfor increasing a likelihood of an occurrence of an arrhythmia in theheart of an animal test subject, said method comprising the steps of:inducing a myocardial infarction in the heart of the test subject;selecting a portion of the myocardium of the test subject whereinhyperinnervation is effective for increasing the likelihood of thearrhythmia; and stimulating myocardial hyperinnervation in the selectedportion of the myocardium of the test subject.
 16. A method forincreasing a likelihood of an occurrence of an arrhythmia in the heartof an animal test subject, said method comprising the steps of: creatingan AV block in the heart; selecting a portion of the myocardium of thetest subject wherein hyperinnervation is effective for increasing thelikelihood of the arrhythmia; and stimulating myocardialhyperinnervation in the selected portion of the myocardium of the testsubject.